This invention is directed generally to chroma demodulators for use in color television receivers, and particularly to chroma demodulators fabricated with integrated circuit technology.
Most modern color television receivers employ chroma demodulators that are built on an integrated circuit chip. In such demodulators, the incoming chroma signal is demodulated by utilizing a locally generated 3.58 MH.sub.z oscillator signal to develop the R-Y, B-Y, and G-Y color-difference signals. Typically, such demodulation is effected by including one pin on the chip to receive the chroma signals and two more input pins to receive oscillator injection signals of the proper phase for demodulating the R-Y and B-Y signals. The G-Y signal is then developed by suitably matrixing the R-Y signal with the B-Y signal.
An alternate demodulation system may employ three separate demodulators, one for each of the R-Y, B-Y and G-Y signals. By including a separate demodulator for the G-Y signal, it becomes more convenient to matrix the color-difference signals with the luminance (Y) signal on the same chip to produce the R, B, and G signals.
One drawback which exists when three separate demodulators are employed is that the demodulator chip must, at least according to existing technology, include yet another input pin for receiving an oscillator injection signal to demodulate the G-Y signal. The use of an additional pin on the chip necessarily increases its cost. Hence, employing existing oscillator injection methods for separately demodulating the R-Y, B-Y and G-Y signals is undesirable, if not impractical.